<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../js/vue.js"></script>

</head>

<body>
    <div id="root">
        姓: <input type="text" v-model="firstName"> <br>
        名: <input type="text" v-model="lastName"> <br>
        全名: <span>{{fullName()}}<span>
    </div>

</body>

</html>
<script>
    new Vue({
        el: '#root',
        data: {
            firstName: '张',
            lastName: '三'
        },
        methods: {
            fullName() {
                return this.firstName + '-' + this.lastName
            }
        }
    })
</script>